1. Field of the Invention
The present invention relates to an optical-integrated unit and an optical pickup device, and particularly to an optical-integrated unit and an optical pickup device that are used for reading and/or writing information from/onto an optical record medium.
2. Description of the Background Art
In general, an optical pickup device is used for reading or writing information from or onto an optical record medium of a disk-like form. Optical record mediums called a CD (Compact Disk) family have been used for reading or writing information with only light. A semiconductor laser element emitting a laser beam of an infrared wavelength having an oscillation wavelength band of 780 nm is used for reading or writing information from/onto the CD family.
In recent years, such optical record mediums are being used in large quantity that are called a DVD (Digital Versatile Disk) family and allow reading and writing with the light and magnetism. The DVD family can record more information than the CD family, and a semiconductor laser element that emits a laser beam of a red wavelength having an oscillation wavelength in a band from 630 to 690 nm is used for reading or writing information. Therefore, such an optical pickup device has been demanded and developed that can read and/or write the information from/onto both the optical record mediums of the CD family and the DVD family.
For example, in a conventional optical pickup device, a first semiconductor laser element emitting a laser beam of an oscillation wavelength of 650 nm and a second semiconductor laser element emitting a laser beam of an oscillation wavelength of 780 nm are arranged in one package. A first transparent substrate is arranged on the package. On the first transparent substrate, the device is provided with a hologram element and a three-beam grating that diffract only a laser beam emitted from the first semiconductor laser element. Also, a second transparent substrate is arranged on the first transparent substrate. On the second transparent substrate, there is arranged a hologram element that diffracts only the laser beam emitted from the second laser element.
In the conventional optical pickup device, the hologram element on the second transparent substrate diffracts a reflected laser beam that is emitted from the first semiconductor laser element and is reflected by the optical record medium, and thereby directs the laser beam to a light-receiving element. The hologram element on the first transparent substrate diffracts the laser beam that is emitted from the second semiconductor laser element and is reflected by the optical record medium, and thereby directs the laser beam to the light-receiving element (see, e.g., Japanese Patent Laying-Open No. 2000-076689).
Also, a conventional diffraction device includes a first hologram provided at its surface with a first hologram grating, and also includes a second hologram that is provided at its surface with a second hologram grating, is arranged on the first hologram and covers the first hologram grating. An area of a surface of the first hologram on the second hologram side is larger than that of a surface of the second hologram on the first hologram side.
In the conventional diffraction device described above, the second hologram is arranged on the first hologram in the following manner. First, a droplet of ultraviolet curing resin (which will be referred to as “UV resin” hereinafter) is dropped onto a position on a surface of the first hologram corresponding to each apex of the second hologram on the first hologram side. Thereafter, the second hologram is placed and optical adjustment is performed. Then, the UV resin is irradiated with the ultraviolet rays for provisional fixing. Then, the UV resin is applied to a portion of the surface of the first hologram that is not in contact with the second hologram, and is also applied to a lower portion of a side surface of on the second hologram. The UV resin is irradiated with the ultraviolet rays so that the second hologram is fixed to the first hologram (see, e.g., Japanese Patent Laying-Open No. 2002-072143).
In another conventional optical pickup device, first and second hologram substrates are integrated with each other. The first and second hologram substrates have a hologram portion for focus detection and a strip hologram portion for track detection. In this conventional optical pickup device, the optical axis adjustment and offset adjustment are performed with the second hologram substrate arranged on the first hologram substrate. Thereafter, the first and second hologram substrates are fixed and integrated by an adhesive. In this process, the adhesive is applied to portions of the first and second hologram substrates through which the laser beam emitted from a light source does not pass. Also, the adhesive is applied to a side surface of the second hologram substrate. Thereby, the first and second hologram substrates are integrated by adhesion (see, e.g., Japanese Patent Laying-Open No. 2002-279683).
In a still another optical pickup device in the prior art, the first and second semiconductor lasers are adjacent to each other. This conventional optical pickup includes a three-beam grating that produces three beams for tracking control, a second hologram element that diffracts the beam of the second semiconductor laser and directs it to a photosensor, a composite polarization beam splitter reflecting only the beam of the first semiconductor laser, and a first hologram element diffracting the beam of the first semiconductor laser and directing it to the photosensor. The first and second hologram elements diffract the light beam of at least one of the wavelengths separated by an optical path separating element (see, e.g., Japanese Patent Laying-Open No. 2002-092933).
In the prior art described above, the two semiconductor laser elements of different oscillation wavelengths are adjacent to each other, and are located such that the optical axes of the laser beams emitted from the respective semiconductor laser elements may be located in substantially the same positions, and thereby the laser beams emitted from the two semiconductor laser elements may enter both the first and second hologram elements. The respective light receiving regions for signal detection must be located as close as possible to each other so that the above different laser beams may be reflected by an information-bearing surface of the optical record medium, and may be received by the common light receiving region.
In the above prior art, the laser beams pass through the two different hologram elements. For obtaining a desired signal, therefore, it is necessary to prepare optical elements such as hologram elements that are optimized by employing wavelength selecting properties or determining laser polarizing directions different from each other. However, such optical elements are expensive, and thus the optical pickup device becomes expensive.